1. Field of the Invention
The present invention relates to the production of magnesium ammonium phosphate slurries. More particularly, the invention relates to magnesium ammonium phosphate hexahydrate slurries having a particle size of about 2 to 7 microns and monohydrate slurries having a particle size of less than about 8 microns.
2. Description of the Related Art
Magnesium ammonium phosphate is a known, naturally occurring mineral which exists in a number of forms, including the hexahydrate form (xe2x80x9cstruvitexe2x80x9d) and the monohydrate form (xe2x80x9cdittmaritexe2x80x9d). The production of solid forms of magnesium ammonium phosphate are known and are used for purposes such as fertilizer, nutrients for cultured growths, treatment of waste water, and treatment of animal waste. For these uses, the magnesium ammonium phosphate is usually manufactured and supplied in dry granular form. The dry granular form may be used for a number of purposes, e.g., broadcast as a fertilizer.
Magnesium ammonium phosphate has a low solubility in water and the dry granular magnesium ammonium phosphate may be dispersed in water to produce a slurry. In the past, all known slurries of magnesium ammonium phosphate have a particle size of at least about 10 microns or larger. There are a number of shortcomings with slurries having this particle size, e.g., the magnesium ammonium phosphate settles out of suspension, poor consistency when dispersed, and poor control over reactions when magnesium ammonium phosphate is a reactant.
Accordingly, a need has arisen for magnesium ammonium phosphate hexahydrate slurries having a particle size of about 2 to about 7 microns and monohydrate slurries having a particle size of less than about 8 microns. This significantly reduces settling and provides for improved consistency and reaction with other compounds.
In accordance with the present invention, a method of producing magnesium ammonium phosphate hexahydrate and monohydrate slurries is provided that significantly reduces the particle size and thereby improves the settling, consistency and reaction with other compounds. The process is composed of the following steps: first, using a magnesium hydroxide supply having very small particle size, a water/magnesium hydroxide slurry is formed. Second, an ammonium source is added. Third, while maintaining an ammonia excess and controlling the temperature to a maximum of about 110xc2x0 F., phosphoric acid is added. This produces a hexahydrate slurry. The hexahydrate slurry may be converted to a monohydrate slurry by heating to the boiling point in the presence of excess water at atmospheric pressure or heating to the boiling point while maintaining a very moderate hydrostatic pressure.
Accordingly, an object of the present invention is to provide magnesium ammonium phosphate hexahydrate slurries having a particle size in the 2 to 7 micron range and monohydrate slurries having a particle size of less than about 8 microns which provides for the advantages of reduced settling, improved consistency when dispersed and improved reaction with other compounds.